ence between the stagnation and static pressure was measured directly with the pressure transducer. (The static pressure was the submergence of the tube, 1.5 in.) For the range of velocities used in the program, the pressure coefficient was independent of velocity. It is apparent from Figure 1 that as the concentration of the polymer is increased beyond a certain value, the sensitivity of the impact tube is drastically decreased. This effect is more pronounced for the smaller flattened tube, 3S, as reduction in the pressure coefficient is noted for concentrations greater than 25 wt. p.p.m. For the larger flattened tube, 2S, reduction is not noted until the concentration exceeds 100 wt. p.p.m. The response of the tube with a hemispherical head, 1R, was essentially the same as that of the larger flattened tube. It is felt that the effect noted here is not due to purely viscous effects, as the trend is in the opposite direction from that previously reported ( 4 ) for viscous Newtonian fluids. Also, the apparent viscosities of the aqueous polymer solutions were not greatly different from water.
The results indicate that extreme caution must be exercised in utilization of impact tubes in the measurement of velocity in polymer solutions. More extensive investigations should be carried out to clarify further the observed phenomenon. ACKNOWLEDGMENT This work is part of a more extensive study on boundary layer flows of dilute polymer solutions sponsored by the Department of the Navy, David Taylor Model Basin under Contract Nonr 710 ( 71 ).